It is known to utilize lubricants in the processing of thermoplastic synthetic resins, inter alia, to lower the required processing temperature. In particular, lubricants have been proposed in the manufacture of rigid sheeting from PVC on heated rolls and calenders.
Among such lubricants, are polyethylene hard paraffins and the oxidized polyethylene waxes prepared therefrom by oxidation. The nonpolar, polyethylene hard paraffins are incompatible with PVC and therefore display a strong external lubricating effect. The oxidized polyethylene waxes which are more or less polar, depending on thier oxidation degree, are compatible with PVC to a certain extent. Consequently, such polyethylene waxes not only exhibit an external lubricating effect but also usually improve the flow characteristics of unplasticized-PVC melts.
Similar to the oxidized polyethylene waxes proper, also suitable as PVC lubricants are such waxes which have been esterified with a polyhydric alcohol, e.g. ethylene glycol. However, apart from a slightly higher light transmission, from which a somewhat better compatibility can be derived, such polyethylene waxes esterified with ethylene glycol differ only insubstantially in their behavior toward unplasticized PVC from non-esterified polyethylene waxes as described in DAS No. 2,201,862.
The comparative test summarized in Tables 1 and 2 confirms this fact. In this case, an oxidized polyethylene wax "A" is compared, in two different PVC test formulations, with the corresponding, glycol-esterified polyethylene wax "A Esterified". The technical properties of "A" and "A Esterified" correspond to the lubricants disclosed in DAS No. 2,201,862:
"A" with osmometric molecular weight of about 1,300, acid number of 63, saponification number of 112, dripping (liquefying) point of 106.degree. C. PA0 "A Esterified" with acid number of 32, saponification number of 109.
TABLE 1 ______________________________________ Test Formulation: ______________________________________ 100 parts by weight of bulk PVC (K value 58) 0.5 parts by weight of organotin compound (stabilizer) 1.0 part by weight of lubricant ______________________________________ Plasticizing Max. Torque Period Light Trans- (Brabender (Brabender mission Plastograph) Plastograph) (2 mm Plates) ______________________________________ "A" 24.6 Nm 3.3 min 68% "A 24.1 Nm 3.3 min 74% Esteri- fied" ______________________________________
TABLE 2 ______________________________________ Test Formulation: ______________________________________ 100 parts by weight of emulsion PVC (K value 80) 0.5 parts by weight of diphenyl thiourea (stabilizer) 4.0 parts by weight of lubricant ______________________________________ Force as Function of Number of Revolutions with Constant Nip Width (Measuring Rolling Mill) ______________________________________ "A" 39 kN "A Esterified" 39 kN ______________________________________
As a result there is no expectation of any advantages resulting from the esterification step.